Method and system for detecting wheel flats on rail vehicles

ABSTRACT

A system and method for detecting the presence of wheel flats on rail vehicles. The system includes a voltage source, one side of which is connected to a first rail of a track and the other to a second rail extending parallel with the first rail in a manner whereby the current circuit includes the rim of the wheel being sensed. The connection points are spaced in the longitudinal direction of the track such that the distance between the connection points is shorter than the smallest axle distance occurring in the vehicle. The circuit also includes an impedance and a detecting means connected over a portion of the impedance to sense changes in voltage resulting from a break in the circuit caused by a wheel flat.

United States Patent [1 1 Bernhardson et al.

[4 1 Oct. 29, 1974 METHOD AND SYSTEM FOR DETECTING WHEEL FLATS ON RAILVEHICLES [75 I Inventors: Rume Bernard Bernhardson,

Skarholmen: Karl Lennart Lundfeldt, Alusjo; Karl-Erik Ullerfors,Hagersten, all of Sweden [73] Assignee: Telefonaktiebolaget L. M.

Ericsson, Stockholm, Sweden [22] Filed: Oct. 2, 1972 [21] Appl. No.:294,251

Related U.S. Application Data [63] Continuation-impart of Ser. No.135,600, April 20,

I 1971, abandoned.

[30] Foreign Application Priority Data Apr. 22, 1970 Sweden 5547/70 [56]References Cited UNITED STATES PATENTS 733,698 7/1903 Church 246/1282,590,603 3/1952 Gieskieng 246/169 R Primary Examiner-M. Henson Wood,Jr. Assistant Examiner-George H. Libman Attorney, Agent, or FirmStevens,Davis, Miller & Mosher [57] ABSTRACT A system and method for detectingthe presence of wheel flats on rail vehicles. The system includes a voltage source, one side of which is connected to a first rail of a trackand the other to a second rail extending parallel with the first rail ina manner whereby the current circuit includes the rim of the wheel beingsensed. The connection points are spaced in the longitudinal directionof the track such that the distance between the connection points isshorter than the smallest axle distance occurring in the vehicle. Thecircuit also includes an impedance and a detecting means connected overa portion of the impedance to sense changes in voltage resulting from abreak in the circuit caused by a wheel flat.

9 Claims, 23 Drawing Figures PAIENTEUUCI 29 mu 3844.513

SHEET 2 or e /0 L ;zJ .l I

L t g EVALUATION MEANS 3; SCHMITT J rALARM TRIGGER l INDICATOR 30 3! 3.3-l l VOLTAGE 3/, 1 T 7 1 GENERATOR 0, I? fi- 277 -55 or I V METHOD ANDSYSTEM FOR DETECTING WHEEL FLATS ON RAIL VEHICLES This is acontinuation-in-part of application Ser. No. 135,600 filed Apr. 20,1971, and now abandoned.

The present invention relates to a method and a system for detectingwheel flats on the rims of rail vehicles, particularly railway cars.

The term wheel flat is used herein to define irregularities in, or theflattening of, the rim of a rail car wheel. Such wheel flats may besustained, for example, when a wheel is braked and slides on itssupporting rail. ln ad dition to the constant pressure applied by thewheel, wheel flats cause the rail to be subjected to dynamic forces andimpact stresses, the magnitude of which depends on the size of the wheelflat, the mass and the speed of the wheel and the weight acting thereon.These dynamic forces can be relatively high and are liable to result indamage to the rails, particularly in winter time at low temperatures,when the rails are brittle and subjected to high tension stresses. Wheelflats can also cause damage to the rolling stock.

It is therefore extremely important that wheel flats be discovered asearly as possible, so that those cars having sustained wheel flat damagecan be taken out of service and repaired.

A number of method have been proposed for detecting wheel flats.

According to one known method, sound from a passing train is recordedand the sound caused by the impact between a wheel flat and thesupporting rail is distinguished by detecting the sound effect orfrequences in the sound. This method, however, does not provide apractically acceptable solution.

Another method known in the art is one in which the accelerations in therail caused by a passing wheel are measured. 1f a wheel which hassustained wheel flat damage rotates at speeds above a certain value, thewheel will release the portion of the rail opposite the flat. Thisrelease causes accelerationsin the rail with different signs on bothedges of the flat.

A further method known in the art is one in which the changes in forcecaused by a wheel flat on the rails are measured by means of straingauges placed along the rails.

These latter, known methods have the disadvantage that a number ofsensing elements, strain gauges or the like, must be placed along therail in order that the accelerations and force changes in the rail canbe measured with the requisite accuracy irrespective of where the wheelflat is located on the rim of the wheel. This also requires acomplicated evaluation apparatus.

Moreover, as will be discussed more thoroughly hereinafter, the latter,known methods also have the disadvantage that the determined magnitudevaries, not only with the size of the wheel flat, but also with theprevailing axle load, i.e., the load on the wheel, which considerablycomplicates an evaluation of the measuring valthe rail is included inthe circuit, and by detecting a break in the current circuit caused by awheel flat.

The invention also relates to a system for putting the method of theinvention into effect, the system being mainly characterized by avoltage source having one terminal connected to a first rail of thetrack and another terminal connected to a second rail extending parallelwith said first rail, e.g., the other rail of the track, in a mannerwhereby the current circuit includes the peripheral surface of the wheelto be sensed, and wherein the connection points are arranged in spacedrelationship with respect to each other in the longitudinal direction ofthe track, said spacing being less than the smallest axle distanceoccurring in the vehicle.

The voltage source may be a DC source of an AC source. When an AC sourceis used, an impedance is preferably connected to the circuit so that thecircuit forms a resonance circuit which is tuned to the frequency of thevoltage source.

A break in the current circuit as the result of a wheel flat can bedetected by sensing the voltage over a portion of the impedance or byinductively sensing the current in the current circuit.

One important advantage afforded by the method and the system of thepresent invention is that the axle load has considerably less affect onthe result of the measurement when compared with the previously knownmethods. Moreover, the detection of wheel flats can be effected toadvantage with the method and system of the present invention at normaltrain speeds, km/h and above, which is not so, for example, with methodsin which the force changes in the rail are measured. A

Under certain assumptions, including a certain minimum speed of thevehicle, the time (t,) during which the wheel loses contact with therail, inter alia due to the presence of a wheel flat, can be expressedby the formula:

where 1 the length of the flat,

v the vehicle speed; i.e., the speed of the center point of the wheel, Mtotal mass of car and load divided by number of axles, I K r'g (l/m 1/2m,), where m is the rigid mass of the axle, r the wheel radius and m,the virtual mass of the rail's mobile part. With m 1,500 kg, m, 800 kgand r 0.5, which is the normal values on these variables in practice,

By inserting t 1/v the relationship t/!, 1.5, for a mass per axle of M16,000 kg at a speed of 72 km/h, and the relationship t/t, variesbetween 6.8 percent when the mass per axle (M) varies between 8,000 and20.000 kg.

When applying a method in which the length of a wheel flat is determinedindirectly by the prior art method of measuring the acceleration in therail, it is found that for the same numerical values on m, m, and r themeasuring result will vary by i 22 percent at a speed of 72 km/h whenthe mass per axle varies between 8,000 and 20,000 kg.

The prior art method which involves determining the additional energy inthe rails also has the disadvantage that it is strongly dependent on theaxle load. In a described embodiment of the method (Rangiertechnik, No.27, 1967) the axle load is therefore measured over separate measuringchannels and the measured value is stored for later correction in thefinal measurement of the wheel flat. It is presumed herewith, however,that the speed of the train is reduced between 20 and 40 km/h during themeasuring process, in contradistinction to the method proposed accordingto the present invention, wherein measurements can be made to advantageat normal train speeds (70 km/h and more).

The invention will now be described in more detail with reference to anembodiment thereof illustrated in the accompanying drawing, in which:

FIG. 1 is a diagrammatic view of a railway track and two pairs of wheelsof a train unit illustrating the principle of the invention.

FIGS. 2A 2E illustrate an embodiment of a system for detecting wheelflats with associated diagrams of electrical signals.

FIGS. 3A 3F illustrate another embodiment with associated diagrams ofelectrical signals.

FIGS. 4A 4F illustrate a further embodiment with associated diagrams ofelectrical signals.

FIGS. 5A 5D illustrate an embodiment including an auxiliary rail withassociated electrical signal diagrams.

FIG. 6 shows a schematic diagram of an evaluation means and alarmindicator used in the present invention.

In FIG. 1 there is illustrated diagrammatically a railway trackconsisting of two rails 10, 11. A train unit moving on the track l0, 11is illustrated by means of two pairs of wheels l2, l3 and l5, 16 havingrespective axles l4 and 17. For detecting wheel flats, such as at 18 onwheel 13, a voltage source 19 is connected to the track 10, 11 over animpedance 20 in a manner whereby one side of the voltage source 19 isconnected to a first rail 11 of the track at a connection point 21 andits other side is connected with the other rail of the track at aconnection point 22. Evaluation equipment 23 is connected over theimpedance 20, or a part thereof.

As will be evident from the following, FIG. 1 illustrates only one ofmany conceivable embodiments of a system for detecting wheel flats, butthe examplary embodiment is particularly suitable for illustrating theprinciple of the invention.

The connection points 21 and 22 to the rails 11 and 10 respectively areoffset with respect to each other when viewed in the longitudinaldirection of the rails 10, II. A pair of wheels 12, 13, which travel tothe right, for example, as seen in FIG. I, approach and pass theconnection point 21 to the rail 11. The pair of wheels 12, I3 and theaxle 14 then close a circuit from the voltage source 19, via theconnection point 21, the rail 11, the wheel 13, the axle 14, the wheel12, the rail 10, the connection point 22 and the impedance 20. Thiscircuit remains closed providing that no wheel flat is present on any ofthe wheels l2, 13. If, however, one of the wheels l2, 13 has sustained adefect, such as a wheel flat 18, the circuit will be broken momentarilyas a result of the wheel 13 releasing" the rail 11 at the wheel flat 18.This break in the circuit is detected by means of the evaluationequipment 23 in a manner hereinafter described.

As will be evident from FIG. 1, current also flows through surroundingwheel pairs, such as 15, 16, 17. To

eliminate extraneous influence on the measuring result. i.e., on thecurrent conditions in the current circuit 19, 21, 11, 13, 14, 12, 10, 22and 20 and back to 19, the rails 10, 11 may, of course, be cut andprovided with insulating joints at the connection points 22 and 21,although this is an unnecessarily expensive and impractical solution. Ashereinafter described with reference to preferred embodiments of thesystem for detecting wheel flats, there is used instead an auxiliaryrail, with which DC or AC voltage can be used, or there is used withembodiments similar to that illustrated in FIG. 1 a relatively highfrequency AC voltage, the impedance 20 being so adapted that the currentcircuit, including the rails 10, 11 and the wheel pairs 12, l3, 14 formsa series resonance circuit at the frequency in question. It should benoted herewith that the current circuit between the connection points21, 22 is not changed electrically, provided that a fault free wheelpair is located between the connection points 21, 22, since the totalrail length through which the current flows is constant and equal to thedistance in the longitudinal direction of the track between theconnection points 21, 22. The resonance condition is thus maintained aslong as a fault free wheel pair is located on the measuring distance,which is defined as the portion of the track 10, 11 located between theconnection points 21, 22.

The inductance in the rails 10, 11 increases relatively quickly outsidethe connection points 21, 22 whereby the influence on the currentconditions from surrounding wheel pairs, such as will be evident fromthe following description as 15, 16, 17 is reduced to a considerableextent. In addition, influence from surrounding wheel pairs can befurther reduced, by not using the high frequency current fed to thetrack primarily for detecting purposes, but instead using the currentwhich is induced in specially arranged coils by the current fed to thetrack.

The distance between the connection points 21, 22 when seen in thelongitudinal direction of the track must be less than the smallest axledistance occurring in the train unit, since otherwise two wheel pairsmay be simultaneously located within the measuring distance, wherebypossible defects in one wheel pair may be short-circuited" by the otherwheel pair. In the case of carriages provided with bogies and withspecial carriages adapted for heavy loads, for example, the smallestaxle distance is often less than the circumference of the wheel and inthis case the measuring distance must be divided into two or more partdistances, which are displaced with respect to each other in thelongitudinal direction of the track in a manner whereby an individual,preferably non-overlapping portion of the periphery of the wheel issensed through each part distance.

The manner in which the measuring distance is divided into partdistances and the distance between said part distances is naturallydetermined beforehand with knowledge of the rolling stock to be movedthrough the section in question.

Railcar wheels have a circumference of approximately 3 m. The axledistance in a bogie, however, is only 2.5 m and, hence, with respect tobogie carriages the measuring distance must be divided into two partdistances of approximately 1.5 m each with an interspace of n'3 m, wheren is a whole number preferably equal to 0 or 1. On certain track systemsspecial carriages or tracks are used having an axle distance of 1.5

m and in this instance the measuring distance must be divided into threepart distances of l m each. The interspace between the part distancesmay be'selected in a number of ways, provided that one portion of thewheel rim is sensed through each of the three part distances. Theinterspaces between the part distances are also in this instanceselected preferably to n-3 m with n equal to a whole number preferably 0or I.

Even though the distance between the connection points 21, 22 ispreferably selected so that said distance is of the same order as, butslightly smaller than, the smallest axle distance occurring in the trainunit, it can be made less and even equal to 0, whereby the connectionpoints 21, 22 are located opposite each other. The detection of possiblewheel flats 18 is made somewhat more difficult in this instance,although the advantage is gained whereby a number of sensing means 1923, which, for example, use separate frequencies, can be placed adjacentto each other, thereby enabling the full wheel circumference to besensed on a track distance of approximately the length of the wheelcircumference irrespective of the axle distances.

The location of the measuring distance on the track section is naturallyimportant. The train unit should travel along the measuring distancewithout it being necessary to brake to any appreciable extent or toaccelerate, and the measuring distance should be placed on a straightsection of track, since when the train section is driven round a curvethe wheel flanges often rest against the rails and may thus shortcircuit a possible wheel flat.

A number of embodiments of the system for detecting wheel flats will nowbe described in more detail with reference to FIGS. 2 5.

FIG. 2A illustrates an embodiment of the detecting system and FIGS. 282E show diagrams of the func tion of the system according to FIG. 2Awith electric signals occurring thereon as a function of the position ofthe wheel axle b-c on the track 10, 11.

The signal voltage from a voltage generator 30 having a frequency f isamplified in an amplifier 31 and fed via a cable 32 and a transformer 33to a series resonance circuit consisting of a secondary inductance L ofthe transformer, an impedance 34 and the impedance in the current pathportions between the points a and b (rail) b and c (the wheel axle andthe transition resistances between wheel and rail), 0 and d (rail) andthe impedance in the connection lines. Since the connection points a andd are displaced in relation to each other in the longitudinal directionof the tracks 10, 11, with a fault-free wheel, the impedance in theseries resonance circuit is not dependent on the position of the wheelaxle be within the measuring distance, which is defined by the lines ahand dg. The current through L and thereby the voltage over the impedance34 only have their maximum value, corresponding to series resistance,when a wheel axle b,c is located within the measuring distance and thetwo wheels are in contact with the rails and 11, respectively.

A part voltage is taken out from the impedance 34, amplified in anamplifier 35, rectified in a rectifier 36 whose output voltage isidentified by the reference U and sensed by a Schmitttrigger or limiter37, which triggers when the wheel pair bc approach the measuringdistance, as shown in FIGS. 2B and 2C. If a wheel having a flat islocated within the measuring distance, contact between wheel and rail isbriefly broken by the flat and the voltage U, drops to beneath thethreshold value of the Schmitt limiter.

Rail contacts SKI and SKZ actuated by one of the wheels in the wheelpair are placed at the points h and d and transmit signals for startingand stopping an evaluation means 38. The passage time, corresponding tothe distance ah-gd, for the whole wheel perimeter or for the part of thewheel perimeter sensed (e. g., half the wheel perimeter) can bedetermined in the means 38 as shown in FIG. 2D. The passage time can bedetermined in the evaluation means 38 by means of suitable logictogether with the time during which the voltage U,, as a result of awheel flat, FIG. 2E, has fallen beneath the threshold level duringpassage of the wheel.

If the quotient between this time, FIG. 2E, and the time for the sensedportion, FIG. 2D, exceeds a certain limit value corresponding to amaximum permitted wheel defect, an alarm, e.g., an acoustic and/orvisual signal, is transmitted from an alarm indicator 39. This quotientwill not vary with the speed v of the train unit, but depends solely onthe size of the wheel flat and, as aforementioned, to a certain extenton the axle load. The alarm indicator 39 may be arranged at a distancefrom the remainingmeasuring equipment, e.g., in the nearest signal box.Subsequent to obtaining a signal from the evaluation means 38 to theeffect that a wheel has sustained flat damage in excess of permittedlimits,

provided with an appropriate number of registering totalizers so thatseveral wheel flats in the same train unit can be detected.

An oscillator may be incorporated in the evaluation means 38 to serve asa reference for the time measurement effected therein. Alternatively,the signal from the generator 30 may be utilized as the reference.

As aforementioned, for the purpose of serving a possible remainingportion or portions of the wheel circumference, identical equipment maybe arranged in spaced relationship, the spacing being so adapted thateach portion is sensed per se without overlapping of said portions.

As will be seen from FIG. 2B, the signal U, does not fall to zero in thepresence of a wheel flat, owing to the shunting effect caused by thesurrounding wheel pairs. The threshold or switch level of theSchmitt-limiter 37 can be set, however, so that the influence exerted bythe shunting effect does not reach the evaluation means 38. Theinfluence exerted by the shunting effect caused by the surrounding wheelpairs may also be reduced by increasing the Q-value of the seriesresonance circuit L, abcdg, 34, which may be effected by appropriateselection of components.

Because the frequency f of the generator 30 is relatively high,preferably of the order of KHZ, disturbances from the railway tractioncurrents (e.g., I6 Hz) and other low frequency signals, e.g., fromdomestic networks (50 Hz) are suppressed. The frequency f is alsoadjusted to the inductances appearing in the current circuit L, 34,abcdg.

FIGS. 3A 3F illustrate another embodiment of a system for detectingwheel flats, corresponding units being identified with the samereference as those shown in FIG. 2A.

A signal voltage from the generator 30 having a frequency f is fed tothe track in same manner as with the system illustrated in FIGS. 2. Theabsolute value of the voltage U over the impedance 34 as a function ofthe position of a wheel pair on the distance between the defining lineso-j and i-k is shown in FIG. 38.

Four coils, Spl, Sp2, Sp3, Sp4 are provided for detecting the currentconditions in the circuit L, abcd, 34, the coils being arranged alongthe rails 10, 11 and the turns of the coils lying horizontally. Voltagesare induced in the coils if a current passes through the rail sectionalong which the coils are placed. The coils Sp2 and Sp3 are placed alongthe whole rail section on the measuring distance, which is defined bythe lines ah and dg. The coils Spl and Sp4 are relatively short and areplaced outside the measuring distance ahdg at the points h and g.

As illustrated in the lower portion of FIG. 3A, the coils Spl Sp4 areconnected in series, and the resulting induced voltage e,+e +e +e wheree, is the voltage induced in coil 1 etc., is amplified in the amplifier35, rectified in the rectifier 36, whose output voltage is shown by U,as shown in FIG. 3C, and is sensed by the Schmitt-trigger 37. Theabsolute values of the voltages e e and e, are equally great for thesame induced current in the rails 10 and 11 along the whole coil.Moreover, the coils Spl Sp4 are connected in series in such a way thatfor the same direction of the induced current, e, is counter-directionalto e, and e;, is counterdirectional to e,. For all axles which arelocated in positions outside the measuring distance ah-dg at anarbitrary distance thereform, no resulting input voltage to amplifier 35(2e is obtained, owing to the current which is fed from the generator 30into the track and which flows through the axles. If a wheel pair islocated, for example, at oj in FIG. 3A, the current flowing through thewheel pair will pass the whole coils Spl and Sp2 in the rails but notone part of the coils Sp3 and Sp4. The resulting induced voltage is thusclose to zero, theoretically equal to zero, since the coils Spl and Sp2are counter-directed and no voltage is induced in the coils Sp3 and Sp4.In a corresponding manner, the total voltage induced in the coils Spland Sp2, Sp3, Sp4 is close to zero for wheel pairs located to the rightof the line dg as seen in FIG. 3A, for example, at ik, since the coilsSp3 and Sp4 balance each other. On the other hand, a constant voltage isobtained from an axle having a faultless wheel pair on the measuringdistance, irrespective of its position between ah and dg, since nocontribution is then obtained from Spl and Sp4 and e +e constant (e kab, e k cd). The two counter-connected coils Spl and Sp4 are notrequired for the actual detection of the current conditions in thecurrent circuit L, abcd, 34, but, as will be evident from the diagram ofthe voltage U as shown in FIG. 3C, the influence exerted by wheel pairslocated outside the measuring distance ah-dg is reduced practically tozero by means of the coils Spl and Sp4, whereby the reliability of thesystem in operation is considerably increased.

The signal reaches the switch level of the Schmitttrigger 37 just beforethe wheel has passed SKI and falls below this level subsequent to thewheel passing 8K2 as shown in FIG. 3D. If a wheel which has sustainedflat damage passes the measuring distance, the

contact between the rails is broken as a result of the flat and thevoltage U below the re-trigger level.

The time taken for the sensed portion of the wheel circumference topass, i.e., the time taken to move from SKI to 8K2 in FIG. 3E, and thetime during which the circuit is broken by the flat, FIG. 3F, arecompared in the evaluation means 38, as with the aforedescribedarrangement illustrated in FIGS. 2A, 2E, and possible defects areindicated on the alarm indicator 39.

As with the previous embodiment, identical equipment must be arranged inspaced relationship for possible remaining portions of the wheelcircumference, the spacing being adapted so that each portion is sensedindividually without overlapping.

A further system for detecting wheel flats is illustrated in FIGS. 4A4E, like parts being identified with like references.

The signal voltage from the generator 30 having the frequency f is fedto the track in the same manner as with the embodiments of FIGS. 2 and3. The absolute value of the voltage U, over the impedance 34 as afunction of the position of a wheel pair on a distance between theboundary lines o-j and i-k is illustrated in FIG. 4B.

The coil Sp5, the turns of which are arranged in a vertical plane, isequally as long as the measuring distance, defined by the lines ah anddg, and is placed centrally between the rails 10, 11. The voltage e, isinduced in the coil by a current passing through the wheel axle be whena wheel pair is located in the vicinity and within the measuringdistance ah-dg. The voltage e is amplified in the amplifier 35,rectified in the rectifier 36, whose output voltage is U as shown inFIG. 4C, and is sensed by the Schmitt-trigger 37.

The signal reaches the threshold level of the Schmitttrigger 37 justbefore the wheel passes SKI and falls below this level after the wheelhas passed SK2, as shown in FIGS. 4C and 4D.

The influence exerted by wheel pairs located outside the measuringdistance ah-dg can also be reduced with the exemplary embodiment bymeans of extra coils, such as the coils Sp6 and Sp7 indicated by dashlines in FIG. 4A, the extra coils being placed outside the coils SpS,when seen in the longitudinal direction of the tracks 10, 11, andconnected in series with the coil Sp5 to the input of the amplifier 35in a manner whereby the voltages, which are induced in the coils Sp6 andSp7 as a result of the current in the illustrated wheel axle, aredirectionally opposed to the voltage e induced by the same current inthe coil SpS.

When a wheel having a wheel flat passes the measuring distance, contactwith the rail is broken by the flat and the voltage induced in the coilSpS falls beneath the threshold level.

The time taken for the sensed portion of the wheel circumference to passSKl, SKZ in FIG. 4E, and the time during which the circuit is broken bythe flat, FIG. 4F, is compared in the evaluation means 38 in the samemanner as that described with reference to the embodiments of FIGS. 2and 3.

As with previous embodiments, identical equipment must be arranged inspaced relationship for any possible remaining portion or portions ofthe wheel circumference, the spacing being adjusted so that each portionof the wheel circumference is sensed individually without overlapping.

Thus, with the illustrated embodiment a current which flowsperpendicular to the longitudinal direction of the tracks l0, 11 issensed. This has the advantage of reducing the influence from disturbingcurrents moving parallel with the tracks 10, I1, although the influencefrom the current in the supply lines to the points a and b in the rails11 and respectively and to the coils SpS, Sp6, Sp7 must be eliminated.These supply lines, considered as magnetic field generating currents,are parallel with the wheel axle b, c in at least one section, andcurrents in the lines can give rise to troublesome disturbances. Onemethod of reducing these disturbances is to place such line portionswhich extend parallel with the wheel axle at a long distance from themeasuring distance ah-dg. Another possibility is to magnetically screenat least the portions of the supply lines which are parallel with thewheel axle.

An embodiment of the evaluation means and the alarm indicator will bedescribed more in detail with reference to FIG. 6. In FIG. 6, theevaluation means 38 and the alarm indicator 39 have been indicated withthe broken lines and the inputs SKI, SK2, and U2," respectively, referto the corresponding outputs from the rail contacts SKI, SK2 and fromthe Schmitttrigger 37, respectively. The evaluation means 38 contains aretriggerable monostable flip-flop circuit MVl, the trigger input ofwhich can receive an activating signal from the rail contact SKI. Abistable flip-flop circuit BVI is also connected with its set inputs tothe rail contact SKI, the reset input r of theflip-flop BVl beingconnected to the rail contact SK2. In the circuit shown in FIG. 6 it ispresupposed that the logic is such that the monostable flip-flops areset to their l-state by an activating signal going from the l-state tothe 0-state and that the bistable flipflops are set to their l-state,i.e., the output is activated when an activating signal going from itsl-state to its 0-state appears on the set input s. The l-output of thebistable flip-flops is inactivated when a signal going from its l-stateto its 0-state appears on the reset input r of the bistable flip-flops.

When a wheel pair is passing the rail contact SKI, i.e., the line ah inthe FIG. 2A 4A, an activating signal will be sent to the flip-flop BVlso that the output I of both flipflops MVl and BVI will be activated.When the wheel pair has passed the line gd in FIG. 2A 4A an activatingsignal (a stop signal) will be sent from the rail contact SK2 to thereset input r of the flip-flop BVl thus disactivating the output 1" ofthis flip-flop. Due to the fact that the set inputs s of the flip-flop8V] is connected to the rail contact SK] and the reset input r of thesame flip-flop is connected to the rail contact SK2, the output I of theflip-flop BVl will be activated as long as a wheel pair is situatedbetween the rail contacts SK] and SK2.

The input U2 is connected to the Schmitt-trigger 37 (FIG. 2A 4A), thevoltage U2 thereby appearing across the input of the inverter ll. PGdenotes a pulse generator which delivers a pulse formed voltage with thefrequency f on one hand to a frequency divider FD and on the other handto an input of an inverting andgate G2, the other two inputs of whichare connected to the output of the inverter I1 and to the output of thebistable flip-flop BVl, respectively. The frequency divider FD dividesthe frequency f of the signal from the pulse generator PG by a factor Xwhich is equal to the quotient between the measuring distance ah-gd andthe maximum permitted length of a wheel flat registered.

For example, a measuring distance of 3 meters and a registered length ofa wheel flat 003 meter will give a factor X 3/003 100. The output of thefrequency divider FD is connected to one input of an inverting and-gateG1, the second input of which is connected to the output I of theflip-flop BVl.

The units EM and BR2 each consist of a binary counter, the outputs ofwhich are connected in pairs to .a comparator circuit K. This circuitcarries out a comparison between the counting position of one counter,

BRl and the corresponding counting position of the other counter BR2, adifference in two corresponding counting positions resulting in anactivating signal being delivered to one input of an inverting andgateG3 if the counting position of BR2 is greater than BRI. The second inputof the gate G3 is connected to the output of a monostable flip-flop MV2which is triggered by the stop signal delivered from the rail contactSK2. Thus, when such a stop signal occurs, an activating signal from thecomparator circuit K can be delivered to the bistable flip-flop BV2,which thereby delivers a 1 signal to the indicator 39 for releasing analarm signal.

The two inputs of an inverting and-gate G5 are connected via an inverterl2 and I3, respectively to the 1" output of the bistable flip-flop BV]and to the I output of the monostable flip-flop MV2, respectively. Theoutput of the inverting and-gate G5 is connected to an input 01 and 02,respectively, of each of the counters BR] and BR2, so that when a 0signal appears on the output of the gate G5, the counters BR] and Br2are zero-set. ln dependence on the output pulses from the gates G1 andG2 which pulses are delivered as clock pulses to the clock input cll andcl2, each of the counters BRl and Br2 is stepped forward. Thus, as longas the output signal from the l output of the flip-flop 8V] is activatedand no output signal from the output l of the flip-flop MV2 is present,and the output signal from the gate G5 is l pulses from the and-gates G1and G2 can be delivered to the counters BRl and BR2 thus causing thesecounters to step forward. When a stopping pulse from the rail contactSK2 is being delivered, the flip-flop MV2 will be set so that its output1 is activated. Simultaneously the flip-flop BVl is reset so that itsoutput is 0. After an additional time interval t the output of flip-flopMV2 is again 0." Therefore the inputs to the inverting gate G5 is l andits output is 0." The counters BRl and BR2 are thus zero-set.

When a wheel pair passes across the line ah (FIGS. 2A 4A), an activatingpulse is delivered from the rail contact SKl to the flip-flops MVl andBVl, bringing them to their 1 state. Due to the fact that a reset pulseto the flip-flop BVl is not delivered until the rail contact SK2delivers an activating pulse, i.e., when the wheel pair has passed theline dg, the output of the flipflop BVl will be l as long as a wheelpair is located between the rail contacts SKl and SK2. During the timethat the output of the flip-flop BVl is I set, stepping pulses can bedelivered to the counter BRl from the frequency divider FD. The counterBRl will thus count the time elapsed for a wheel passage between thelines ah and gd (i.e., the measuring distance).

The condition for the gate G2 to give stepping pulses from the pulsegenerator PG to the counter BR2 is:

i. the output of the flip-flop BV I is 1" set, i.e., a wheel pair haspassed the line ah.

ii. the voltage U2 across the output of the Schmitttrigger should below, i.e., a wheel flat has been detected and is passing over the railsection hd or ag (or both).

If these two conditions are accomplished, then stepping pulses aredelivered from the pulse generator PG to the counter BR2 and the timefor a wheel flat break is being measured. The counter ER! is beingstepped forward by pulses with the frequency f/X, the counter BR2 isbeing stepped forward by pulses with the frequency f and a comparisonbetween the contents of the two counters is carried out. This means thatif no wheel flat has been detected and thus no signal to open the gateG2 has been obtained, then no pulses has been delivered to the counterBR2, and the counting position of BR2 is less than that of BRl. Becausethe output from the comparator K is then no activation of flip-flop BV2can take place and its output is therefore 0. On the contrary, if awheel flat of length greater than the maximum permitted value has passedthe section ah-gd, the counting position of BR2 is greater than that ofER] and the comparator K will give the output I. At the passage of thesection end (gd), SK2 activates MV2 and the corresponding input to theinverting gate G3 is l." Thus flip-flop BV2 is activated to its l state,giving a 0" input to alarm flip-flop BV3 of alarm indicator unit 39through inverter I5. This in turn activates alarm lamp LA and summer SUthrough amplifler F. The l output from BV2 is also fed to inverting gateG4, whose second input is already I," originating from SK2 throughinverter I4. The binary counter AR (axle counter) is therefore steppedforward through the monostable flip-flop MV3, activated by G4, by SK2and this is repeated for each succeeding axle since the l" output fromflip-flop BV2 remains due to the alarm" setting of comparator K.

The monostable flip-flop MV3 has a pulse duration t;, which is chosenless than the time interval to the next wheel passage of rail contactSK2. Thus MV3 will be reset before the next stop pulse from SK2. Theoutput from retriggerable monostable flip-flop MVl resets to 0"approximately sec (or any other convenient time interval) after a wheelhas passed SKI and no additional wheel has actuated SKI during thses 10seconds. Thus the output of BV2 is reset to 0 closing G4. No furtheraxles can then be counted by AR. However, the setting of BV3 and hencethe alarm indication remains. The axle-mumber indication of AR alsoremains. After observation the units BV3 and AR can be reset manuallythrough actuators mr l and mr 2 respectively.

The rail contacts SK] and SK2 used in the embodiments illustrated inFIGS. 2A, 3A and 4A, and which may also be used in the embodimentillustrated in FIG. 5A, for connecting and disconnecting the evaluationequipment and for determining the period of time during which a wheel islocated within a measuring distance ah-dg, can be in the form ofcontacts actuated mechanically or electrically by the-passing wheel. Itis also possible to use, however, additional coils placed on the linesah and dg respectively, e.g., adjacent, or instead of the coils Spl, Sp4or the coils Sp6, Sp7 which sense the current flowing through a passingwheel pair. The voltages induced in the additional coils may, forexample, control Schmitt-triggers or limiters which are set so that theevaluation equipment 38 is connected and disconnected when the wheelpair passes the lines ah and dg.

FIGS. 5A 5D illustrate an embodiment of the system for detecting wheelflats in which an electrically conductive auxiliary rail 40 and 41mounted to each rails 10, 11 is utilized for sensing the two wheels 43,44 in a wheel pair.

FIG. 5B is a diagrammatic sectional view of the rails 10, 11, the wheel43, 44 and the auxiliary rail 40, 41. The rail 40, 41 is insulated andis also preferably yieldingly mounted to the rail 10, 11 by means of arubber suspension means 42 or the like.

Voltage sources for AC or Dc current 51 and 52 are connected between therails 10 and 11 and the auxiliary rail 40 and 41 mounted externally ofeach rail 10, 11.

The current through the current circuit, including the rim of the wheel43, 44, is measured easiest over an impedance 53 and 54 connected inseries with rails and auxiliary rails, although inductive sensing of thecurrent can also be used in this instance.

FIGS. 5C and 5D show the voltages U and U over the impedances 53 and 54when a defect and a faultless wheel respectively pass the measuringdistance. In the former case the circuit is broken by the flat and thecurrent falls momentarily to zero, FIG. 5C.

The time taken for the wheel or a specific part of the wheel to pass andthe time during which the circuit is broken by the flat are compared inthe evaluation means 55 and 56. If the magnitude of the flat exceedspermitted limits, the fault indicator 39 transmits an acoustic and/or avisual alarm signal and the position of the axle in the train isregistered by a counter device.

In this embodiment, the distance between the connection points to therails 10, 11 and the auxiliary rails 40, 41 is naturally not critical,since the measuring distance is totally determined by the auxiliaryrails 40, 41.

As with previous embodiments, identical equipment must be arranged inspaced relationship for possible remaining portion or portions of thewheel circumference, the spacing being adjusted so that each portion ofthe wheel circumference is sensed individually without overlapping.

Rail contacts, similar to SKI and SK2 in the embodiments of FIGS. 2 4,can also be arranged to advantage with the embodiment of FIGS. 5A 5D, atthe end points of the measuring distance for connecting anddisconnecting the evaluation equipment 55, 56. In this respect theauxiliary rail 40, 41 can be extended beyond the measuring distance sothat contact between the wheel 43, 44 and the auxiliary rail 40, 41 isstable when measuring is commensed.

The arrangements illustrated in FIGS. 1 5 thus constitute preferredembodiments of a system for detecting wheel flats according to theinvention. It is obvious, however, that only minor modification of theevaluation means and the alarm indicator is required for the describedarrangements to operate simultaneously as a so-called axle counter. Thereduction in the influence exerted by the surrounding wheel pairs,obtained with the aforedescribed arrangement, is in this case a greatadvantage. The system according to the invention, can also be usedsolely as an axle counter, the measuring distance 21 22, ah-dg,preferably being made short so that disturbances from the surroundingwheel pairs and the axles, are further reduced.

The invention is not restricted to the illustrated and describedembodiments thereof but can be modified within the scope of thefollowing claims.

What is claimed is:

l. A method for detecting wheel flats on rail vehicles having wheelsmade of electrically conductive material and an axle between oppositelysituated wheels, comprising the steps of: passing an alternating currenthaving a relatively high frequency through a current circuit whichincludes a first and a second wheel to be sensed and the axle betweensaid wheels, said first and second wheels being the only wheels in saidcurrent circuit wherein a contact point between the peripheral bearingsurface of each wheel and the associated rail together with a portion ofa first and a second rail forms part of the circuit, and detecting achange of the current amplitude in the current circuit caused by thepresence of a wheel flat on at least one of said wheels.

2. A method according to claim 1 wherein the step of detecting comprisesdetecting the current conditions in the current circuit inductively.

3. A system for detecting wheel flats on rail vehicles having aplurality of pairs of electrically conductive wheels, the wheels of eachpair being situated on respective rails of a track and connected by anaxle, comprising: a current circuit, having a high frequency alternatingvoltage source connected to the rails of the track, wherein the circuitincludes the peripheral bearing surface of each wheel of the pair ofwheels to be sensed and the axle, and wherein one side of thevoltages'ource is connected at one point to a first rail in the trackand the other side of the voltage source is connected at a second pointto a second rail in the track extending parallel with the first rail andwherein the connection points are spaced apart from each other in alongitudinal direction of the track, said spacing being shorter than thesmallest distance between adjacent axles occurring in the vehicle; andmeans, connected to the circuit, for indicating wheel flats.

4. A system according to claim 3 wherein the distance in thelongitudinal direction of the track between the connection points of thevoltage source is less than or equal to the circumference of a wheel tobe sensed.

a the resistance being applied to the indicating means for indicatinginterruptions in the current circuit.

6. A system according to claim 5 wherein the indicating means comprisestwo contacts, arranged in spaced relationship with respect to eachother, and actuated by a passing wheel for, respectively, connecting anddisconnecting, the indicating means.

7. A system for detecting wheel flats on rail vehicles, having aplurality of pairs of electrically conductive wheels, the wheels of eachpair being situated on respective rails of a track and connected by anaxle, comprising: a current circuit including an AC voltage sourceconnected to the rails of a track, the peripheral surface of each wheelof the pair of wheels to be sensed, the axle and an impedance which isadjusted so that the circuit containing the impedance, the rails, theaxle and the wheels forms a resonance circuit tuned to the frequency ofthe voltage source, and wherein one side of the voltage source isconnected at one point to a first rail in a track and the other side ofthe voltage source is connected at a second point to a second rail inthe track extending parallel with the first rail and wherein theconnection points are spaced apart from each other in a longitudinaldirection of the track, said spacing being shorter than the smallestdistance between axles occurring in the vehicle; and means connected tothe circuit, forindicating wheel flats.

8. A system according to claim .7, wherein the indicating means isconnected over a portion of the impedance to sense the voltage changesoccurring as a result of a wheel flat.

9. A method for detecting wheel flats on rail vehicles having wheelsmade of electrically conductive material and an axle between oppositelysituated wheels, comprising the steps of: passing an alternating currentthrough a current circuit whichincludes a first and a second wheel to besensed and the axle between said wheels, wherein a contact point betweenthe peripheral bearing surface of each wheel and the associated railtogether with a portion of a first and a second rail forms part of thecircuit, generating a first signal corresponding to a first period oftime, detecting, during said first period of time, a change of thecurrent amplitude in the current circuit caused by the presence of awheel flat on at least one of said wheels and generating a second signalcorresponding to the time the wheel fiat is detected, comparing saidfirst and second signals, and generating an alarm signal if thecomparison indicates the wheel fiat is in excess of a predeterminedlimit.

1. A method for detecting wheel flats on rail vehicles having wheelsmade of electrically conductive material and an axle between oppositelysituated wheels, comprising the steps of: passing an alternating currenthaving a relatively high frequency through a current circuit whichincludes a first and a second wheel to be sensed and the axle betweensaid wheels, said first and second wheels being the only wheels in saidcurrent circuit wherein a contact point between the peripheral bearingsurface of each wheel and the associated rail together with a portion ofa first and a second rail forms part of the circuit, and detecting achange of the current amplitude in the current circuit caused by thepresence of a wheel flat on at least one of said wheels.
 2. A methodaccording to claim 1 wherein the step of detecting comprises detectingthe current conditions in the current circuit inductively.
 3. A systemfor detecting wheel flats on rail vehicles having a plurality of pairsof electrically conductive wheels, the wheels of each pair beingsituated on respective rails of a track and connected by an axle,comprising: a current circuit, having a high frequency alternatingvoltage source connected to the rails of the track, wherein the circuitincludes the peripheral bearing surface of each wheel of the pair ofwheels to be sensed and the axle, and wherein one side of the voltagesource is connected at one point to a first rail in the track and theother side of the voltage source is connected at a second point to asecond rail in the track extending parallel with the first rail andwherein the connection points are spaced apart from each other in alongitudinal direction of the track, said spacing being shorter than thesmallest distance between adjacent axles occurring in the vehicle; andmeans, connected to the circuit, for indicating wheel flats.
 4. A systemaccording to claim 3 wherein the distance in the longitudinal directionof the track between the connection points of the voltage source is lessthan or equal to the circumference of a wheel to be sensed.
 5. A systemaccording to claim 3 wherein the current circuit comprises a resistance,the voltage drop over the resistance being applied to the indicatingmeans for indicating interruptions in the current circuit.
 6. A systemaccording to claim 5 wherein the indicating means comprises twocontacts, arranged in spaced relationship with respect to each other,and actuated by a passing wheel for, respectively, connecting anddisconnecting, the indicating means.
 7. A system for detecting wheelflats on rail vehicles, having a plurality of pairs of electricallyconductive wheels, the wheels of each pair being situated on respectiverails of a track and connected by an axle, comprising: a current circuitincluding an AC voltage source connected to the rails of a track, theperipheral surface of each wheel of the pair of wheels to be sensed, theaxle and an impedance which is adjusted so that the circuit conTainingthe impedance, the rails, the axle and the wheels forms a resonancecircuit tuned to the frequency of the voltage source, and wherein oneside of the voltage source is connected at one point to a first rail ina track and the other side of the voltage source is connected at asecond point to a second rail in the track extending parallel with thefirst rail and wherein the connection points are spaced apart from eachother in a longitudinal direction of the track, said spacing beingshorter than the smallest distance between axles occurring in thevehicle; and means connected to the circuit, for indicating wheel flats.8. A system according to claim 7 wherein the indicating means isconnected over a portion of the impedance to sense the voltage changesoccurring as a result of a wheel flat.
 9. A method for detecting wheelflats on rail vehicles having wheels made of electrically conductivematerial and an axle between oppositely situated wheels, comprising thesteps of: passing an alternating current through a current circuit whichincludes a first and a second wheel to be sensed and the axle betweensaid wheels, wherein a contact point between the peripheral bearingsurface of each wheel and the associated rail together with a portion ofa first and a second rail forms part of the circuit, generating a firstsignal corresponding to a first period of time, detecting, during saidfirst period of time, a change of the current amplitude in the currentcircuit caused by the presence of a wheel flat on at least one of saidwheels and generating a second signal corresponding to the time thewheel flat is detected, comparing said first and second signals, andgenerating an alarm signal if the comparison indicates the wheel flat isin excess of a predetermined limit.